The incorporation or integration of mechanical, electrical and optical components into integral devices has created enormous demands on material processing. Furthermore, the individual components integrated in the devices are shrinking in size, for certain application. At the same time, performance expectations are increasing. Therefore, there is considerable interest in the formation of specific compositions applied to substrates with desired selected compositions and properties. Interest in forming highly uniform materials for these coatings has sparked the development of corresponding processes.
As a particular example, optical components can be integrated onto a planar chip-type base similar to an electronic integrated circuit. By placing the optical components onto an integrated chip such as a silicon wafer, many optical components can be squeezed into a very small footprint. For the mass production of these integrated optical chips, existing semiconductor technology, such as lithography and dry etching, can be involved advantageously in appropriate steps of the production process. Other optical applications include, for example, formation of displays and the like. Similarly, integrated electrical components can be formed along a substrate surface and may involve crystalline and/or amorphous materials. Certain dielectric materials can have electrical and/or optical applications.
Electrochemical cells in general involve reduction-oxidation reactions in separated half-cells that are appropriately connected for ionic flow as well as electron flow across an external circuit. Batteries and fuel cell produce useful work in the form of the electron flow across a load generated from the reduction-oxidation reactions. In other electrochemical cells, a load is applied to the cell to induce desired chemical reactions at the electrodes to form desired chemical products. Fuel cells differ from batteries in that both the reducing agent and the oxidizing agent can be replenished without dismantling the cell. Fuel cells and in some cases batteries can comprise individual cells stacked in series to increase the resulting voltage. Adjacent cells connected in series can have an electrically conductive plate, e.g., a bipolar plate or electrical interconnect, linking adjacent cells. Since the reactants of a fuel cell can be replenished, appropriate flow paths can be integrated into the cell.
Several types of fuel cells have gained recognition as distinct classes of fuel cells that are distinguishable from each other due to the nature of their construction and the materials used in their construction. Particular fuel cell designs introduce specific challenges in material performances. Common features generally found in different fuel cell designs involve the flow of fuel and oxidizing agent for long-term performance with appropriate design consideration for heat management, electrical connection and ionic flow. Different fuel cell designs differ from each other in the construction of the electrodes and/or electrolyte, which separates the electrodes, and in some cases the particular fuel. Many fuel cell designs operate with hydrogen gas, H2, although some fuel cells can operate with other fuels, such as methanol or methane. Coatings can be useful for the formation of functional and/or structure components of fuel cells.
Several approaches have been used and/or suggested for the commercial deposition of the functional coating materials. These approaches include, for example, flame hydrolysis deposition, chemical vapor deposition, physical vapor deposition, sol-gel chemical deposition and ion implantation. Flame hydrolysis deposition has become the leader for commercial implementation of planar optical waveguides. Flame hydrolysis and forms of chemical vapor deposition have also been successful in the production of glass fibers for use as fiber optic elements. Flame hydrolysis deposition involves the use of a hydrogen-oxygen flame to react gaseous precursors to form particles of the optical material as a coating on the surface of the substrate. Subsequent heat treatment of the coating can result in the formation of a uniform optical material, which generally is a glass material.
Flame hydrolysis deposition is efficient, but cannot be easily adapted to obtain more uniform coatings. Chemical vapor deposition involves the deposition of radicals, molecules and/or atoms onto the substrate surface rather than particles. Chemical vapor deposition can achieve very uniform materials, but the process is extremely slow. If attempts are made to increase the rates using chemical vapor deposition, the film quality is compromised, which reduces the advantage of the chemical vapor deposition process for applications in which uniformity is an important criterion.
At the same time, approaches have been developed using laser pyrolysis for the production of highly uniform submicron and nanoscale particles with a wide range of compositions. Highly uniform particles are desirable for the fabrication of a variety of devices including, for example, batteries, polishing compositions, catalysts, and phosphors for optical displays. Laser pyrolysis involves an intense light beam that drives the chemical reaction of a reactant stream to form highly uniform particles following the rapid quench of the stream after leaving the laser beam.